Signal box



FIG. 1 is a front, right, and top perspective view of a signal boxshowing my new design;

FIG. 2 is a front elevational view thereof, the rear elevational viewbeing identical to the front elevational view;

FIG. 3 is a right side elevational view thereof, the left sideelevational view being identical to the right side elevational view;and,

FIG. 4 is a top plan view thereof.

The ornamental design for a signal box, as shown and described.